The present invention relates to a limited slip differential for transmitting drive differentially to two spaced apart wheels on a vehicle, such as the opposite ends of a drive axle, which may be driven round corners or on skidding surfaces, on-road or off-road.
It is desirable to allow the two wheels to rotate at somewhat different speeds without losing drive torque to either, for instance while cornering or having different tire pressures or tire loadings. Standard differentials serve this purpose well, but if one wheel loses adhesion, e.g. on soft sand or on ice, spin-outs can occur and effective traction can be lost by the driving torque becoming applied only to the skidding or spinning wheel.
The differential housing of a typical drive axle differential is rotationally driven about the axis of the two driven ground wheel shafts. The housing rotates the axles of one or more freely rotating bevel pinions and these engage two side bevel gears rotating with the respective wheels.
An arrangement to allow some but not excessive slip would be thus most desirable. One prior art differential for cars and small trucks senses excessive differential action by responding at low speeds independently (with a fly weight) to a threshold speed difference and bypassing differential action by clutching either or both output axles to the differential housing. This can be unsuited to heavy goods vehicles (HGV's) with high rotating inertias to control. Other attempts propose that the differential gearing driving tooth contactings in the bevel gearing pinion and side gears be not simply root-to-tip but partly transversely across the tooth faces. The resulting variable radius of the contact point is claimed to increase friction between the housing bearing carrying the side-gears and wheel shafts, by increasing the axial thrust always exerted on the driven member in a bevel drive. Even a modest increase in friction (not total locking) is usually quite adequate to regain enough traction to exit the area of unfavorable ground surface. These prior art limited slip/locking differentials operate automatically. Other proposed differentials can be locked by the driver, which leads to damage if the locking is applied impatiently during a spin-out or if not disengaged after use.
The present invention proposes the use of a unique rotational irregularity which causes a desired pulsating action (which increases bearing or clutch friction sufficiently during spin-outs) which will interfere very little with low speed differencing during cornering, and operates satisfactorily on heavy duty vehicles.